title: Magnetic and spectroscopic investigation of thermally and optically driven valence tautomerism in thioether-bridged dinuclear cobalt-dioxolene complexes.
abstract: A series of dinuclear cobalt complexes of general formula [Co(Mentpa)(diox-S-diox)Co(Mentpa)](PF6)2·MeOH (n = 0, 2, 3) was prepared through the synthesis of the bis-bidentate ligand 6,6'-((1,4-phenylenebis(methylene))bis(sulfanediyl))bis(3,5-di-tert-butyl-benzene-1,2-diol) (diox-S-diox). The ancillary ligands Mentpa are obtained by the tripodal tris(2-pyridylmethyl)amine (tpa) ligand through successive introduction of methyl groups into the 6 position of the pyridine moieties. As expected, the steric hindrance induced by this substitution modulates the redox properties of the metal acceptor, determining the charge distribution of the metal-dioxolene adduct at room temperature. Magnetic measurements and X-ray photoelectron and X-ray absorption spectroscopies indicate that the charge distributions low-spin-Co(III)-catecholate and high-spin-Co(II)-semiquinonate characterize the complexes formed by the tpa and Me3tpa tetradentate ligands, respectively. The complex formed by the Me2tpa ligand undergoes a thermal- and light-induced interconversion of the two states, in agreement with the existence of a valence tautomeric equilibrium. All complexes were stable and behaved reproducibly under X-ray irradiation. This work points out a fast and simple chemical approach to structurally and electronically modify the catechol ring while leaving its coordination capabilities unaffected. These findings afford a robust chemical method to prepare sulfur-functionalized dioxolene ligands as new molecular bricks for chemical functionalization of noble metal surfaces with this class of molecular switches.
authors.affiliation: Laboratory of Molecular Magnetism (LaMM), Dipartimento di Chimica 'Ugo Schiff', Università degli Studi di Firenze & INSTM RU of Firenze , via della Lastruccia 3-13, 50019 Sesto Fiorentino, Italy.
authors.forename: Giordano
authors.initials: G
authors.lastname: Poneti
authors.forename: Matteo
authors.initials: M
authors.lastname: Mannini
authors.forename: Brunetto
authors.initials: B
authors.lastname: Cortigiani
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Poggini
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Sorace
authors.forename: Edwige
authors.initials: E
authors.lastname: Otero
authors.forename: Philippe
authors.initials: P
authors.lastname: Sainctavit
authors.forename: Roberta
authors.initials: R
authors.lastname: Sessoli
authors.forename: Andrea
authors.initials: A
authors.lastname: Dei